HBV infects the liver and causes an inflammation commonly referred to as viral hepatitis. The disease is endemic in certain populations, such as China and other parts of Asia. About a third of the world's population, more than 2.4 billion people have been infected with the HBV. HBV infection may either be acute, otherwise known as self-limiting, or chronic, otherwise known as long-standing. Acute infection with HBV is associated with acute viral hepatitis, an illness that begins with general ill-health, loss of appetite, nausea, vomiting, body aches, mild fever, dark urine, and then progresses to development of jaundice. The illness lasts for a few weeks and then gradually improves in most affected people. A few patients may have more severe liver disease (fulminant hepatic failure), and may die as a result of it. The infection may be entirely asymptomatic and may go unrecognized. Chronic infection with HBV may be either asymptomatic or may be associated with a chronic inflammation of the liver, chronic hepatitis, leading to liver cirrhosis over a period of several years. This type of infection dramatically increases the incidence of hepatocellular carcinoma. Chronic carriers are encouraged to avoid consuming alcohol as it increases their risk for liver cirrhosis and cancer. Approved medications for treatment of HBV include lamivudine, adefovir, tenofovir, telbivudine and entecavir. However, drug resistance is a main problem of the drug treatment in view of mutations of the HBV genes.
The HBV belongs to the Hepadnaviridae, a group of hepatotropic DNA viruses. HBV is a blood-borne virus, comprising a small, partially double-stranded DNA genome, carrying four extensively overlapping open reading frames, consisting of an inner nucleocapsid, comprising the HBV core protein (“HBcAg”), viral polymerase and viral DNA, surrounded by a membranous envelope containing HBV surface antigens (“HBsAg”). The viral envelope contains three different, but related surface antigen proteins, large (L), medium (M) and small (S), which share a common carboxy terminal region but have different amino termini, arising from variable use of initiation triplets at different points within a continuous open reading frame.
US 20060159705 provides a method for the production of a HBV antigen suitable for use in a vaccine, the method comprising purification of the antigen in the presence of cysteine, to vaccines comprising such antigens. US 20070280962 provides HBV core antigen particles that are characterized by multiple immunogen specificities. US 20110165194 relates to an HBV vaccine comprising an entire hepatitis B virus surface antigen of L protein, M protein and S protein, in which the produced antigens form virus-like particles, and a multi-antigen vaccine further comprising an HBV core antigen in addition to the entire surface antigen, and a method for preparing the same. Although a number of HBV vaccines have been disclosed, most of these vaccines are administered by injection, which need skilled medicians and higher cost. Oral vaccines are more convenient in administration and thus can be widely applies to reduce HBV infection.
Molecular pharming has attracted extensive attention in production of various pharmaceutical proteins, including enzymes, vaccines, antibodies, hormones, etc. Liz Richter et al., Nat Biotechnol. 2000 November; 18(11):1167-71. use tobacco leaves and potato tuber to produce oral HBV vaccine. Edible mushrooms are regarded as appropriate hosts for production of recombinant proteins, especially for the development of edible vaccines. Arakawa et al. use potato leaves and tubers, tobacco leaves, tomato, lettuce and rice to produce cholera vaccine. However, transgenic plants are planted in an open environment, so using transgenic plants for protein production may cause impacts on health and the environment. The use of mushrooms for molecular pharming has all the advantages of plant-based systems coupled with unique benefits including complete duplication, fast growth, scale-up production under controlled conditions and less gene contamination. US 20140123345 provides a truncated glyceraldehyde-3-phosphate dehydrogenase promoter and a construct comprising the promoter of the invention operably linked to a heterologous transcribable polynucleotide molecule and a mushroom comprising the construct. However, this prior art patent application only provides expressible truncated glyceraldehyde-3-phosphate dehydrogenase promoter in mushroom and it still needs extensive research works and overcome technical problems to achieve the purpose of using mushroom as molecular pharming.